Liftable undercarriage system for airplanes



Dec. 14,1943. I R L LEVY I R 2,336,794

LIFTABLE UNDERCARRIAGE SYSTEM FOR AIRPLANES Filed Feb. 10, 1941 Patented Dec. 14, 1943 UNETE rric Rene Lucien Levy, Paris, France, assignor to 'Societe dlnventicns Aeronautiques et Mecaniques S. l. A. l /L. Fribcurg.

Application February 10 In France Bee 4 Claims.

present invention relates to liftable undez'oarriages for airplanes, of the known type according to which the energy necessary for lowering the undercarriage is totally or partially accumulated during the immediately preceding lifting operation. It is particularly applicable to undercarriage systems in which this accumulation of energy is effected by means of a hydropneumatic accumulator cooperating with a lifting jack. Such systems have been initially described in the United States Patent No. 2,001, 520, dated 14, 1935, in the name of Mr. Rene Lucien Levy.

This patent has especially described an embodiment in which the lowering operation is effected in two periods, in such conditions that the major part of the driving energy available at the accumulator is consumed in the final period of the lowering, that is to say, when the gravity moment of the pendular system is the smallest.

Conversely, during a lifting operation, the largest part of the energy consumed in the jack serves to raise the pressure of the accumulator, cburi'rl' a first period, whereas, during the following period, the stress of the jack is mainly used to overcome the resistant stress of the undercarriage.

The above mentioned patent describes in particular an embodiment in which these features result from a certain cable connection between a movable element of the accumulator and the liftable system.

In a general manner, according to the very structure of the liftable undercarriage and according to the location of the extreme positions it must occupy, the curve of the pressure necesto overcome the weight of the system pre sents different features.

In some cases, this curve passes through a maximum for an intermediate position of the undercarriage. The same is then true for the resultant curve of the elementary pressures which necessary for lifting the undercarriage and simultaneously, for increasing the pressure of the accumulator.

The applicant has found that it is advanta geous to avoid that the source of liquid under pressure should be subjected to such peaks.

The present invention allows, in undercarris of the type under consideration, of causthe source of driving power to act throughout lifting operation, according to a pressure we which is exempt from said peaks and which sents a generally favorable rate, for instance,

Switzerland 1941, Serial No. 378,319 ember 21, 1939 a gradual and slight increase of the driving pressure between the initial instant and the final instant of the lifting operation.

For that purpose, the invention consists in associating with the lifting jack (main jack) an auxiliary jack which communicates with the accumulator, as the main jack, but which is kinematically connected to the liftable undercarriage, so as to introduce at every instant, in the hydropneumatic circuit, the desirable pressure com pensation.

The accompanyin drawing (Fig. 1) diagrammatically illustrates the general system of a liftable wheel for airplanes, presenting this feature.

Figs. 2 and 3 are detail views, in section.

The wheel R, pivoting, for lifting, about the axis A, is carried by a strut J on which is pivoted, at a, a brace K, pivoted in its turn to a fixed point I: of the airplane, and capable of folding down about a pivot c, at a suitable point of its length, this entire unit being known per se.

The main jack V, divided into two compartments I 2, by the pitson 1Jthe rod t of which attacks, at c, the pivot of the foldable strutcommunicates, through the conduit 3, with a distributor D, by means of which the compartment 5 can be put in communication with a tank B, or with the delivery of a pump P, exerting a suction in said tank.

A branch pipe 3 of the conduit 3 also connects the distributor D to a box 4 enclosing a locking valve 5, and connected by a conduit 5 to the hydropneumatic accumulator G.

According to the present invention, a compensating auxiliary jack H communicates with said accumulator through a conduit 7, and the movable element of said auxiliary jackin this case, the piston h-is kinematically connected to the pendular system RJin the example by a crank m-so as to introduce at every instant, in the hydropneumatic circuit, the desirable pressure compensation.

During a lifting operation, moving the system RJ in the direction of the arrows, the liquid delivered by the piston 22, from the compartment 2 of the main jack, through the valve 5 and the conduit 5 into the accumulator G, can partly have access to the compartment 8 of the auxiliary jack H. The additional space afforded to the liquid by said compartment 8 progressively varies during the lifting. By suitably securing the crank m on the axis A, said variation will be such that the pressure required from the pump follows a favorable curve, answering, for instance, to a slight and progressive increase between the initial instant and the final instant of the lift- What I claim as my invention and desire to secure by Letters Patent is:

1. In a liftable undercarriage for airplanes, a principal hydraulic jack for operating the undercarriage, an auxiliary hydraulic jack cooperating in the operation, a pipe connecting the principal jack to the auxiliary jack and so arranged that liquid will fiow from the principal jack for the operation of the auxiliary jack during lifting of the undercarriage and from the auxiliary jack to the principal jack during lowering of the undercarriage, a hydro-pneumatic accumulator branched on this pipe.

2. In a liftable undercarriage for airplanes, a principal hydraulic double acting jack for the operation of the undercarriage, a pipe issuing from the compartment of this principal jack corresponding to thelowering of the undercarriage, an auxiliary jack at the extremity of this pipe and cooperating with the working of the gear, said pipe being so arranged that liquid Will be forced by the principal jack into the auxiliary jack for operation of the latter during lifting of the undercarriage and from the auxiliary jack to the principal jack during the lowering of the undercarriage, a hydro-pneumatic accumulator branched on this pipe.

3. Liftable undercarriage for airplanes comprising a strut carrying the wheel and rotatably mounted on an axis, a breakable brace interposed between the strut and the fuselage of the airplane, a principal double acting hydraulic jack attacking the said brace, a crank mounted on the axis of the strut and rigid with the latter, an auxiliary jack attacking this crank and fed by the principal jack, a pipe between the principal jack and the auxiliary jack, said pipe being so connected to said jacks that liquid will be forced from the principal jack to the auxiliary jack for actuating the latter during the lifting of the undercarriage and will be forced from the auxiliary jack to the principal jack during the lowering of the undercarriage, a hydro-pneumatic accumulator branched on this pipe.

4. In an airplane of the type having a liftable undercarriage with a foldable brace pivotally connected to the body of the airplane and to the undercarriage, a piston rod connected to the brace, a main piston on the rod, and a main cylinder in which the piston operates, the improvement comprising an auxiliary cylinder movably connected to the body, a piston in the auxiliary cylinder, a second piston rod connected to the last mentioned piston, a part fixed to the undercarriage and pivotally connected to said second piston rod, a passageway placing the cylinders in communication in such manner that fluid will flow from the main cylinder to the auxiliary cylinder when the main piston rod is actuated to fold said brace and lift the undercarriage and will flow oppositely when the undercarriage is lowered, and a pressure accumulator interposed in said passageway.

RENE LUCIEN LEVY. 

